openinverter forum

Managed to get the link wire soldered today at work. Hopefully I’ll be able to get the he boost converter wired in and test it at the weekend.

Don't forget to test with the light bulb on DC bus first, in case the booster goes haywire.

I haven’t managed to test this yet as I’ve lost my garage space and the weather has been far too cold/wet/snowy over the last two weeks to do any wiring outside! I’ll keep you posted once I’ve had a go at this.

johu wrote: ↑Mon Jan 18, 2021 2:52 pm So this would be the wire to add in order to optionally run booster PWM off TIM4_CH4. It uses the remaining channel of the ULN2003 making it backward compatible. Outputs need to paralleled, making it a wired-OR.

Let me know if you want to try this and I can make the necessary software mods.

Nevermind, wasn't much to change so test firmware attached. When detecting a Prius2 hardware it will clock TIM4 down to 8.8 kHz.

Parametrization:
pwmfunc = speed (2)
pwmofs = -1500
pwmgain = 0.5

The timer top value is 8192, with that it would basically short out the battery input, with 0 it does not boost at all.

So per rpm it would increase the timer value by 0.5. So say at 4096 rpm timer is at 2048 so voltage would be 25% boosted. Since it is not desirable to boost at low rpm you use pwmofs=-1500. Then there will be no boosting until 3000 rpm and then 0.5 digit per rpm. At 10000 rpm booster dutycycle would be 0.5*10000-1500 = 3500. So voltage almost doubled.

Now you can play with booster settings

Finally had the chance to try this.

I'd previously done the PCB changes so today I refitted the boost converter and connected the CPWM pin. I've flashed the new firmware and tested with the wheels off the ground. Nothing went pop but I couldn't tell whether the boost converter was doing anything either.

I'm assuming udc should show the boosted voltage? So I would be able to see the voltage increasing with rpm if it was working?

Is it just the three auxiliary pwm parameters that I need to change?

Unfortunately, I'm in quarantine at home having come back from a work trip abroad so can't go out and test on the road until the weekend.

Yes, udc should show boosted voltage and yes those three parameters govern auxiliary PWM. Can you make a picture of your mods?
You can also set pwmgain=0 and pwmofs = 2048 to generate a 50/50% dutycycle (also works outside run mode). Just check if you see this. CPWM must be pulled up to 12V with 470 Ohm. Be aware that with just that, the input is shorted out by the boost converter. Anyway, with PWM running you should see 1.6V at the ULN input and 6V on its output.

Also I forgot the inverse logic in my parameter example. PWM full on means no boost! So set pwmofs=8192 and pwmgain=-0.5 then boost should kick in above 4096 rpm.

Ah, I missed the bit about pulling up CPWM.

I’ll make sure to check the PWM is working properly then, a shorted battery doesn’t sound fun!

Thanks for the help.

Well, its Toyota so it will just say "sorry Tom-san, I can't do this". But still..
Also limit maximum boost ratio to 50% or so. So set fmax/pwmofs/pwmgain in a way that PWM never drops below 2048 digits

Success!

Added the pull-up resistor and after some fiddling with parameters the voltage now increases with rpm.
Just need to test it on the road, but that will have to wait until Friday when I’m out of quarantine!

Thanks for the help so far.

Finally managed to test this on the road. Nothing went pop and the voltage boosting seems to work perfectly, however it doesn’t seem to help as much as I’d hoped. There is definitely a small improvement to acceleration/top speed but there is still a big drop off in torque above 20mph. With full throttle, it still never pulls any more than 50-60 amps DC so a max power of around 15kW.

I’m going to do some longer drives and more testing to see how usable it is. Unfortunately my DC-DC (Enova not the Prius one) has died so I can’t do much testing at the moment. I’m slightly concerned that the DC-DC dying could be related to boosting the voltage but I can’t see how that would be as it’s connected before the booster. Upon investigation a couple of the big transistors have shorted so it may just be a lack of cooling? It was bolted to the main water cooled heat sink in the enova but it’s now just on a small aluminium plate without any cooling.

Both good and bad then...
Could there be any parameter setting that limits the output current somehow?
I'm very close to getting my car out on the road with the MGR and a 360V batterypack. Doesn't sound to hopeful with your results...

bexander wrote: ↑Fri Apr 02, 2021 4:51 pm Both good and bad then...
Could there be any parameter setting that limits the output current somehow?
I'm very close to getting my car out on the road with the MGR and a 360V batterypack. Doesn't sound to hopeful with your results...

I’ve double checked all the parameters and there shouldn’t be anything limiting the current as far as I can tell. Throtcur is set to 3A/% and I increased both current limits to 500A to make sure it wasn’t that either.

What voltage are you now seeing at top speed?

celeron55 wrote: ↑Fri Apr 02, 2021 8:49 pm What voltage are you now seeing at top speed?

I’ve done limited testing due to the DC DC issue but it is at approximately 450V at 50mph. I did a quick test with the voltage permanently boosted (not linked to speed) to 480V as well. I know Johannes recommended not boosting at low speeds but this seemed to give the best results, what was the reason for not boosting at low speeds?

tom3141 wrote: ↑Sat Apr 03, 2021 8:15 am I know Johannes recommended not boosting at low speeds but this seemed to give the best results, what was the reason for not boosting at low speeds?

I suspect when boosting at low speeds you are limited by the 20kW limit of the DC-DC converter. When it is not running the inductor just acts as a short and shouldn't be limiting power as much.

johu wrote: ↑Sat Apr 03, 2021 11:00 am

tom3141 wrote: ↑Sat Apr 03, 2021 8:15 am I know Johannes recommended not boosting at low speeds but this seemed to give the best results, what was the reason for not boosting at low speeds?

I suspect when boosting at low speeds you are limited by the 20kW limit of the DC-DC converter. When it is not running the inductor just acts as a short and shouldn't be limiting power as much.

When I tested boosting at lower speeds the acceleration was the best I’ve managed up to 20mph. Whatever I’ve tried (both with and without the booster) I have never been able to pull more than 60A at the battery so I’ve never put more than 20kw into the motor anyway.

As I said, once I’ve sorted the DC-DC I’ll do some longer tests and record some plots to try to work out what’s going on.

Practise beats theory then

So... it's turning out using the boost converter makes sense because you can't sink more than 20kW into the motor without it anyway.

Can we figure out how high the voltage would have to be boosted in order for the motor to sink the full 45kW it's designed for? If 450V gives 20kW, it would seem to me you need 675V for 45kW.

That's plausible, but inconvenient.

celeron55 wrote: ↑Sun Apr 04, 2021 6:16 pm So... it's turning out using the boost converter makes sense because you can't sink more than 20kW into the motor without it anyway.

Can we figure out how high the voltage would have to be boosted in order for the motor to sink the full 45kW it's designed for? If 450V gives 20kW, it would seem to me you need 675V for 45kW.

That's plausible, but inconvenient.

Sounds plausible, I guess the rating of 650V given in the Lexus datasheets would add up with this too. I will try increasing the voltage further when I test again but don’t want to get too close to 600V as I think that’s the rating of the main capacitors.

Accordign to the video by Damien where he measures the mg dc-bus voltage it is 500V in the prius while driving. I suspect it is the same for the Lexus. The 650V is the maximum rated of the componentes, and not maximum used.
Still very strange you can't get more than 20kW?

It's not wise to attempt much more than 20kW with this setup because the converter isn't rated for more. A beefier Lexus converter is needed. And I think we don't have replacement logic boards for any yet.

I’m having some issues when turning the car on. I get overvoltage errors and a strange fast clicking sound from the inverter during precharge. It has happened since I added the booster in. I’m wondering whether the PWM could be going to 100% for a few seconds during boot up? It happens no matter what pwm settings I have. Any ideas?

I finally have tested my car with the MGR as well and my results are similar, viewtopic.php?f=11&t=912&p=26527#p26527.

tom3141 wrote: ↑Sat Apr 10, 2021 8:17 pm I’m having some issues when turning the car on. I get overvoltage errors and a strange fast clicking sound from the inverter during precharge. It has happened since I added the booster in. I’m wondering whether the PWM could be going to 100% for a few seconds during boot up? It happens no matter what pwm settings I have. Any ideas?

Oh that is entirely possible. With the pull-up resistor installed the low side gate is closed -> short to battery. In boot loader the PWM is not active, obviously. You'd need to pull the same trick as in charge mode: pull up CSDN and connect it to DCSW signal so it is pulled low (enabled) as soon as you start.

EDIT: what are you AUX PWM settings?

Finally got out for a proper test drive today. I had been having DC-DC issues which were stopping me going very far.

I’ve done the mod Johannes described above to stop the problems when turning on. This now works perfectly.

With the voltage permanently boosted to just over 500V it can maintain 30mph up any incline and maxes out at 55mph on the flat. So it’s useable but not quite what I was hoping for. I think I’ll start to use it for a while and investigate options for improving the performance.

I’m wondering if the boost converter is limited by the inductor reactance and limiting current flow